1. Field of the Invention
The present invention relates generally to gas turbine power plants, and more particularly, to an arrangement for providing liquid coolant to the turbine buckets of the power plant.
2. Description of the Prior Art
It is well known that the efficiency and output of a gas turbine power plant can be increased by increasing the operating temperature of the turbine. As a practical matter, however, the turbine operating temperature is limited by the material properties of the various turbine components exposed to the high temperature. The hot combustion gases combined with fuel contaminants can produce rapid oxidation and corrosion of the components when they are at high temperatures. This is known as hot corrosion. In order to minimize hot corrosion of the materials, the maximum temperature of the components is preferably limited to 1000.degree. F. In order to achieve high operating temperatures it is therefore necessary to provide cooling for critical turbine components such as the turbine buckets.
Where the gas turbine firing temperature is in the range of 2800.degree. F. it is believed that water cooling is well suited for maintaining the temperature of the turbine buckets at levels where thermal stress and resistance to hot corrosion would be acceptable. One problem associated with water cooling of turbine buckets is delivery of the water to the rotating buckets in a uniform regulated manner.
The prior art has broadly considered the flow of liquid coolant to transfer heat from turbine buckets. One of the systems having liquid-cooled buckets is shown in U.S. Pat. No. 3,446,481 to Kydd. The system disclosed in Kydd uses stationary spray nozzles which extend through the turbine vanes and which spray water toward coolant ports in the rotating turbine discs for distribution to the buckets. A sprayed liquid flow is, however, very sensitive and difficult to regulate over the operating range of the turbine. The dynamics of the turbine rotor produce variable axial forces on the coolant spray at different turbine speeds which affect the trajectory of the spray. It is therefore extremely difficult to assure that the spray is properly aimed at the coolant ports over the entire operating range of the turbine. The stationary external supply of liquid coolant also requires indirect regulation of the flow rate in accordance with variations in the turbine speed.
Accordingly, one object of the present invention is to provide an arrangement for a gas turbine in which the rotor is effectively cooled with liquid coolant.
Another object is to provide an arrangement for a gas turbine in which liquid coolant is supplied directly to the rotor through passages in the turbine disc to provide effective cooling over the entire operating range of the turbine.
Another object is to provide an arrangement for supplying liquid coolant to a gas turbine in which the flow of coolant is propelled by centrifugal force and generally self-regulated to accommodate variations in turbine speeds.
Another object is to provide an arrangement for a gas turbine in which liquid coolant is supplied directly to the rotor in a manner that prevents or substantially reduces the possibility of contamination of the coolant with carbon particles or other products of the combustion system.
Still a further object is to provide an arrangement for supplying liquid coolant to a gas turbine from an axial coolant supply passage to provide an effective, self-regulated flow of coolant to the turbine buckets over the entire operating range of the turbine.